A new model for soil organic carbon turnover using bomb carbon

A new model is presented that uses bomb carbon (C-14 enrichment) to calculate the turnover times of active soil organic carbon (SOC). The new approach overcomes major deficiencies of older models, particularly in respect to the C-14 content of carbon input to SOC and of carbon output from SOC. Calculated turnover times of active carbon for ten European forest sites ranged from 4.0 to 15.1 years with a mean of 8.2 years. The model was successfully validated in soil incubation experiments, where the measured (14C) content of (microbially) respired CO2 was on average 9.6% (DeltapM) higher than that of bulk SOC, but agreed considerably well with the modeled C-14 content. Furthermore, we used the model's sensitivity tests to show that over long time periods (decades), soils can only sequester small amounts of carbon.